1. Field of the Invention
The subject disclosure relates to unitized bearing seal assemblies, and more particularly to, a low torque seal assembly which utilizes a highly viscous fluid filled labyrinth path to maintain a seal and exclude contaminants from within an interior bearing chamber.
2. Background of the Related Art
Ball and roller bearing assemblies are well known in the art and have been used for many years in applications such as railway cars, crane wheels, and trucking. Bearing assemblies are typically provided as a self-contained unit and generally include a plurality of circumferentially-spaced balls or rollers confined between concentric outer and inner rings or cylinders. The concentric rings define an interior chamber for containing the rolling elements and supply smooth, hard, accurate surfaces for the balls or rollers to roll on. These surfaces are referred to as races or raceways. A uniform spacing is maintained between adjacent balls or rollers within the interior chamber by a cage or separator element and a lubricant such as grease is applied therein. The rolling elements are the most important component of the bearing assembly, because they transmit the loads from the moving parts of the machine to the stationary support. The balls are ideally uniformly spherical, but the rollers may be straight cylinders, or they may be tapered, cone-shaped or other forms depending upon the purpose of the design. Additionally, the balls or rollers can be provided in a single row or multiple rows.
Bearing assemblies are typically dimensioned and configured such that they can be installed by sliding the assembly over an axle journal and into a housing. The inner ring is typically engaged with the axle journal and the outer ring is engaged with the housing so as to enable the axle to rotate relative to the housing or vise versa. Bearing assemblies often operate in hostile environments, and this is particularly true when they are used in application such as railcars. As a result, the interior chamber which contains the rolling elements, must be sealed so that contaminants, such as dirt and water, are kept out of and lubricant is kept in.
U.S. Pat. No. 4,770,548 to Otto discloses a hydrodynamic seal which is suitable for closing the end of a tapered roller bearing assembly. The seal disclosed therein includes a seal case which is pressed into a counterbore formed in the end of the outer ring (cup) and an elastomeric sealing element. The elastomeric sealing element has a primary lip and a secondary lip which cooperate with a sealing surface on a thrust rib on the inner ring (cone) to effect a live seal along the surface. The secondary lip is in direct contact with the sealing surface of the thrust rib with the primary lip being slightly offset therefrom.
U.S. Pat. No. 4,819,949 also to Otto discloses a seal assembly for closing the end of a tapered roller bearing. The seal assembly disclosed therein is a unitized assembly which includes interlocked seal and shield portions. The seal portion is a two-piece unit which consists of a rigid case and a flexible sealing element. The rigid case is mounted to the outer ring of the bearing and the flexible sealing element is bonded to the outboard end of the rigid case. The flexible sealing element has a dirt lip directed obliquely toward and contacting the shield portion, and a secondary lip also directed obliquely toward the shield portion, but it is not in contact with the shield portion.
Radial lip seals which contact the sealing surface, like those disclosed in the Otto patents, are common. Although contacting lip seals adequately perform the sealing function, the contact between the lip and the sealing surface causes seal wear and a loss of power in the rotating system due to friction between the two surfaces. In addition to the interference between the lip and the sealing surface, the elasticity of the rubber element and the spring force (if used) applied thereto creates a radial load which results in additional torque requirements.
There is a need therefore for a seal assembly which excludes contaminants, such as water and dirt, from within the interior bearing chamber and retains the lubricant therein, while requiring less torque to rotate than a conventional radial lip seal.